Many chemical products are produced in the form of tablets or as fine, dry powders. It is often highly desirable to package pre-determined amounts of such chemicals for ease of utilisation by end users. Typical examples would be in the biocidal and pesticide industries, where specific quantities of particular products are pre-packed for both convenience and safety reasons. Pre-packaging of specified amounts of hazardous products, such as toxic chemicals, reduces operator error and minimises chemical handling risks inherent in further weighing or dilution operations with such chemicals.
In the medical field, the delivery of an accurate, pre-determined dose of medicament to a patient is critical to effective treatment of disease. The majority of drugs are now prescribed to patients in packages containing many unit treatments of particular medicaments. This pre-packaging of known quantities of medicaments facilitates the accurate administration of drugs to a patient by simplifying the process and minimising the risk of patient error. Thus many medicaments are provided in blister packs, where each blister contains a unit dose in tabular or powder form.
Pulmonary drug delivery systems depend upon the administration of effective doses of medicament to the lungs of a patient and rely upon inhalation of a drug dispersion or aerosol. A variety of medical devices are used to administer such medicaments, ranging from nebulisers, metered dose inhalers (MDI's) and dry powder inhalers (DPl's). The latter are of particular interest to the present invention, as they rely upon the delivery of fine dry powders which are often stored within a unit dose receptacle such as a blister pack within the device.
There are many technical problems in filling receptacles, including unit-dose receptacles such as blister packs, with powdered medicament. Fine powders can be difficult to manipulate and measure, particularly when flow properties of the powder vary due to agglomerisation or clumping of the powder. The presence of clumps in powders leads to inaccuracies in the quantities of powder dispensed into receptacles which rely upon gravimetric and/or volumetric methods. Thus the metering of fine powders presents many technical problems in terms of basic handling and weighing/measuring operations associated with dispensing such powders into appropriate receptacles.
Several approaches to addressing these problems are apparent from the literature. Thus U.S. Pat. No. 4,640,322 discloses a device which uses a negative pressure to draw powder from a hopper to a measuring chamber. An alternative method, involving a stirring mechanism, is described in U.S. Pat. No. 2,540,059, wherein powder undergoes stirring prior to pouring into a metering chamber. Other methods range from taking cores from a powder reservoir for filling capsules (U.S. Pat. No. 3,874,431) to applying a vacuum to fill measuring chambers with powder (Canadian Patent Number 949,786).
The Applicant has found that particulate material can be metered onto a first surface of a porous retainer or substrate by the application of a vacuum to a second surface. This method is particularly effective for metering powdered material which has been fluidised by aeration in a fluid powder bed. The particulate material can then be hermetically sealed in place on the porous retainer with a suitable metallic foil, plastic film or organo-metallo laminate, to form a blister or primary pack for use in a DPI device.